Patent GB-514572-A (GB)
Title: Improvements in or relating to the manufacture of gears
IPC: D06B23/00
Filed: 1938-05-10
Abstract: 514,572. Gear-cutting; milling-cutters, GLEASON WORKS. May 10, 1938, No. 13978. Convention date, Dec. 22, 1937. [Class 83 (iii)] In cutting gears by continuous rotation of a cutter having teeth arranged 'part-way only round its periphery with a gap to permit indexing as described in Specification 495,944 between the last and first blades, the cutter blades have side -cutting edges which have the same profile curvature. For bevel gears the variation in tooth depth is obtained by making' the blades of varying height so that they cut to different depths as the cutter is fed along the gear tooth. The tapering tooth space defined by planes 24, 24<1> could be produced' by a milling cutter fed in the direction of line 26 (see also Fig. 6). The curved profiles 30, 30<1> are produced by a milling cutter 35, Fig. 2 in which successive blades have the same curvature, but the centres of curvature are displaced from one another along lines 40, 40<1> parallel to the tangents 24, 24<1>. The cutting surface of the cutter and the tooth surface being produced contact along an inclined line 46, Fig. 6, and for.this reason the cutting profile 48, Fig. 2, produces a more curved tooth profile 50, the increase in curvature depending on the rate of displacement of the centre along line 40 and the inclination of a generator 33 at the point P to the feed direction 26. The centres of curvature for the blades which cut at the small and large end respectively are therefore located at points 39<1>, 38<1> respectively which are not equidistant from the main point 37. Intermediate blades have their centres disposed at points between 38<1> and 39'. In this way the teeth at the small end have considerably greater curvature than the cutting edge of the cutter while at the large end the tooth curvature is only slightly greater than that of the operative cutting edge. The tops of the cutter blades are arranged along a spiral. The cutting edges of the other side of the cutter are similarly arranged and both sides of a gear tooth space are produced simultaneously. The mating gear is produced in a similar way to that described above, the contact between the gear and its mate showing a slight mismatch or relief at the teeth ends. Additional localization of the tooth bearing may be obtained in the manner described in U.S.A. Specification 1,733,326. The cutter for cutting a pinion is shown in Fig. 9. The cutting edges 101, 102, operate at the large and small end respectively and edge 100 operates at the mid. point. Points 105, 106, Fig. 8, are on the line of contact 80 of tooth surface 82 with a plane tangent to 'the tooth' surface at point 86. The blades all have the same radius of curvature but the centres are displaced along a line 107. The varying lengths of the blades are shown at 110-112. A mathematical analysis is given in the Specification for determining the line of instantaneous contact 46 between the cutter and the tooth surface and also the line of contact 115 between a tooth surface and a tangential plane at P. The feed may be either in the same or the opposite direction as the cut. In another modification the feed may be non-uniform. In this case the centres of curvature 38, 39 may be equidistant from the point 37, i.e., the centres of curvature are displaced at a uniform rate along the line 40. In a further modification the feed may still be non-uniform but the centres of curvature displaced at a changing rate from one another. The invention is also applicable to cutting spur and helical gears. The length of the feed movement during the finishing operation is at least 50 per cent. greater than the face width of the gear. In finishing a bevel gear 140, Fig. 15, the cutter, rotating in direction of arrow 145 about a centre 141 as though rolling on a line 148, moves from position 1411 to 141", the extreme lines of contact being shown at 1521, 152<11>. The actual limits of cutter travel are shown at 141a and 141b. If the cutter is a finishing cutter there is a rapid return from 141b to 141a but preferably the cutter effects both roughing and finishing in a single revolution, the roughing during travel from 141b to 141a and finishing during the return to 141b. In an actual embodiment, Fig. 17, the cutters are arranged in segments and are secured to the head by screws 183. The segments 182a to 182b carry roughing cutters preferably of increasing height and the segments from 182d to 182c carrying finishing cutters profiled as described above with their tops arranged along a spiral 187. The roughing blades are also preferably of the same arcuate curvature but are thinner than the corresponding finishing blades. The segments preferably fit against conical shoulders 188 and their end faces engage keys 184 fitting in slots 185 in the head. The feed movement may be accelerated during the latter part of the roughing cut. In another modification, Fig. 20, a stocking cutter 200 is arranged coaxially with a combined roughing and finishing cutter constructed as described above. 201 shows one of the blades of the stocking cutter which are. of gradually increasing height and arranged on part of the cutter periphery only-preferably on a smaller part than the toothed part of the cutter 210. No relief is required on the stocking cutters. A similar stocking cutter may be used for cutting spur gears.